Abrasive tips for ceramic matrix composite blades and methods for making the same

ABSTRACT

A blade and method for producing the blade for a gas turbine engine are described herein. The blade may include a composite airfoil. The airfoil may comprise a ceramic material, and a distal end. A tip may extend from the distal end of the airfoil. The tip of the airfoil may comprise a substantially porous structure and may comprise infiltrated material extending from an airfoil preform to a tip preform to join the airfoil preform and the tip preform.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 14/957,149, filed Dec. 2, 2015, which claims priority to and thebenefit of U.S. Provisional Patent Application No. 62/093,605, filedDec. 18, 2014. The entire contents of each of U.S. application Ser. No.14/957,149 and U.S. Provisional Patent Application No. 62/093,605 areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to gas turbine engines, andmore specifically to ceramic matrix composite components used in gasturbine engines.

BACKGROUND

Gas turbine engine components are exposed to high temperatureenvironments with an increasing demand for even higher temperatures.Economic and environmental concerns relating to the reduction ofemissions and the increase of efficiency are driving the demand forhigher gas turbine operating temperatures. In order to meet thesedemands, the designs of components, such as turbine blades, areincorporating ceramic-containing materials like ceramic matrixcomposites.

Sometimes turbine blades include abrasive tips which may be designed towear away an abradable blade track in a controlled manner. The abradablecoating may be worn away during interaction between the rotating bladesand stationary parts of an engine. Traditionally turbine blade tips mayinclude a metallic alloy. Abrasive tips may be embedded with a particle.Bonding of the turbine blade tip to a compatible superalloy blade mayrequire a layer of nickel. Because of the demand for highertemperatures, ceramic matrix composite components may replacetraditional metallic components, such as turbine blades. One benefit ofceramic matrix composite engine components is the high-temperaturemechanical, physical, and chemical properties of the ceramic matrixcomposite components which may allow the gas turbine engines to operateat higher temperatures than current engines. However, traditional bladetips and coatings may be incompatible with a ceramic matrix compositeblade because of bonding, joining, and manufacturing difficulties.Additionally, there may be thermal-mechanical stresses induced betweenthe traditional coating and the ceramic matrix composite componentduring operation of a gas turbine engine.

SUMMARY

The present disclosure may comprise one or more of the followingfeatures and combinations thereof.

According to an aspect of the present disclosure, a method for making ablade for use in a gas turbine engine is taught. The method may includeforming a tip preform having a continuous porosity substantiallythroughout the tip preform, positioning the tip preform relative to anairfoil preform so that the tip preform may extend from a distal end ofthe airfoil preform, and co-infiltrating, after the positioning the tippreform, the tip preform and the airfoil preform to densify the tippreform and the airfoil preform thereby joining the tip preform and theairfoil preform to form the blade. The airfoil preform may includeceramic material and may have continuous porosity substantiallythroughout the airfoil preform.

In some embodiments, co-co-infiltrating may comprise densifying the tippreform and the airfoil preform via slurry infiltration and meltinfiltration. Co-infiltrating may further comprise densifying the tippreform and the airfoil preform via chemical vapor infiltration orchemical vapor deposition prior to slurry infiltration and meltinfiltration.

In some embodiments, positioning the tip preform relative to the airfoilpreform may comprise inserting the tip preform into a tip-receivingspace that may extend into the airfoil preform from the distal end ofthe airfoil preform. The infiltrated material may extend from theairfoil preform to the tip preform.

In some embodiments, forming the tip preform may comprise mixing tipparticles with a substrate of the tip preform. The tip particles maycomprise silicon carbide. The tip particles may comprise cubic boronnitride, silicon nitride or combination thereof. Forming the tip preformmay comprise encapsulating the tip particles and the substrate in apolymer.

In some embodiments, co-infiltrating the substrate of the tip preformand the airfoil preform may include burning off the polymer. In someembodiments, the airfoil preform may be substantially silicon carbidebased fibers.

According to another aspect of the present disclosure a blade for use ina gas turbine engine is taught. The blade may comprise an airfoilcomprising a ceramic material, a tip comprising a porous structure,extending beyond a distal end of the airfoil, and infiltrated materialthat may extend from the airfoil to the tip to join the airfoil and thetip. It is understood and appreciated that the airfoil may be acomposite and the airfoil and tip may be preforms.

In some embodiments, the infiltrated material of the airfoil may besubstantially identical to the infiltrated material of the tip. In someembodiments, the ceramic material of the airfoil may comprise siliconcarbide, and the tip may comprise silicon carbide. The airfoil mayinclude a tip-receiving space that extends into the airfoil and aportion of the tip may be arranged in the tip-receiving space of theairfoil. The airfoil may include a hollow core in fluid communicationwith the tip-receiving space.

In some embodiments, the tip may further comprise tip particlessuspended in a substrate. The tip particles may include silicon carbide.The tip particles may be selected from cubic boron nitride, siliconnitride, or a combination thereof.

In some embodiments, the porosity of the tip may be between about 1percent and about 10 percent by volume. The tip may have a shape thatgenerally conforms to the shape of the airfoil when viewed from beyondthe distal end of the airfoil.

In some embodiments, the blade may be formed by one of chemical vaporinfiltration; a combination of chemical vapor infiltration, meltinfiltration, and/or polymer-infiltration-pyrolysis; or a combination ofchemical vapor infiltration and/or polymer-infiltration-pyrolysis.

These and other features of the present disclosure will become moreapparent from the following description of the illustrative embodiments

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of a blade made from ceramic matrix materialsand adapted for use in a gas turbine engine showing that the bladeincludes a root, a platform, a composite airfoil, and an abrasive tip;

FIG. 2 is an enlarged view of the blade from FIG. 1 depicting the tipextending beyond the distal end of the of the airfoil;

FIG. 3. is top plan view of the blade from FIGS. 1 and 2 depicting ashape of the tip that generally conforms to the shape of the airfoil ofthe blade; and

FIG. 4 is block diagram of a method for producing the blade shown inFIGS. 1-3.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to a number of illustrativeembodiments illustrated in the drawings and specific language will beused to describe the same.

An illustrative blade 10 adapted for use in a gas turbine engineincludes a tip 12, as shown in FIG. 1. The tip 12 may be abrasive andmay be designed to interact with a blade track having an abradablecoating that surrounds the blade track such that the abrasive tip 12rubs the abradable coating under some operating conditions of theengine. The blade 10 may also include a root 14, a platform 16 coupledto the root 14, and an airfoil 18 coupled to the platform 16. The blade10, the platform 16 and the root 14 may be single piece construction ormay be separate components joined together. The platform 16 may besandwiched between the root 14 and the airfoil 18 and may separate theroot 14 from the airfoil 18 so that gasses passing over the airfoil 18are blocked from moving down around the root 14, as suggested in FIG. 1.The airfoil 18 may be shaped aerodynamically to interact with gasesmoving over the blade 10.

As shown in FIG. 2, the tip 12 may be adapted to extend into a tipreceiving space 34 of the airfoil 18 and may extend out of the tipreceiving space 34 of the airfoil 18. The tip 12 may provide an abrasivesurface including particles 28 designed to wear away an abradable in acontrolled manner during interaction between the rotating blade 10 andstationary parts of an engine (e.g. a blade track). The thickness of thetip 12 may vary based on distance between the rotating component and thestatic components such that the abradable may be worn away during usewithout damage to the airfoil 18.

The tip 12 may include a material substantially identical to a materialused in the airfoil 18, such as a ceramic material. The tip 12 mayinclude at least one material dissimilar to materials in the airfoil 18.In some examples, the tip 12 may include particles such as siliconcarbide. In other examples, the tip 12 may include particles dissimilarfrom the materials of the airfoil 18. The dissimilar particles mayinclude cubic boron nitride, silicon nitride, or a combination thereof.

As shown in FIG. 3, the shape of the tip 36 may generally conform to theshape of the airfoil 18 when viewed from beyond the distal end 22 of theairfoil 18. Illustratively, the tip 12 may have a porosity of betweenabout 1 percent and about 10 percent by volume. The porosity may be ameasure of the void or empty spaces in a material, and is a fraction ofthe volume of voids over the total volume.

The tip 12 may be formed from a tip preform. The tip preform may havecontinuous porosity substantially throughout the tip preform. Continuousporosity may allow a gas or liquid phase to infiltrate into the poresduring infiltration steps. Continuous porosity may be a permeablestructure with open cells for infiltrating materials. The tip preformmay be a layer of particles, fibers, or combination thereof such asceramic particles or ceramic fibers. The fibers may be formed into aweave. The weave may then be stacked to form the preform shape. In someembodiments, the tip preform may include a ceramic foam. The tip preformmay include a ceramic foam adjacent to a layer of particles or fibers.The ceramic foam may be sandwiched between the layer of particles orfibers and the airfoil 10 when the blade 10 is assembled. The tippreform may have a porosity of between about 10% and about 90% by volumesuch that it may be infiltrated in subsequent densification steps.

As shown in FIGS. 1 and 2, in the illustrative embodiment, the airfoil18 of the blade 10, may include a ceramic matrix material and mayinclude ceramic-containing reinforcements. For example, the airfoil mayinclude a plurality of fibers woven into a ply (sometimes called aweave), and the plies 41, 42 may be laid up or stacked on top of eachother to form the airfoil 18. The plies 41, 42 may form a tip-receivingspace 34 at a distal end 22 of the airfoil 18 and a core 20, as shown inFIGS. 1 and 2. The tip-receiving space 34 may extend into the airfoil 18and a portion of the tip 12 may be arranged in the tip receiving space34 of the airfoil 18.

The core 20 may be in fluid communication with the tip receiving space34 of the airfoil 18. The core may be hollow. The core 20 may also allowflow of cooling air and may be in communication with cooling holes 32 a,32 b formed in the tip 12 to transport cooling air through the airfoil18 and thereby maintain the temperature of airfoil 18. In someembodiments, ribs or other support structures may extend through thecore 20.

The airfoil 18 may be formed from an airfoil preform. The airfoilpreform may be fabricated from a preform of ceramic fibers to formplies. The ceramic fibers may be fibers comprising silicon carbide. Theairfoil preform may have porosity between the fibers that may beinfiltrated by an infiltrated material such as silicon metal, siliconcarbide, and/or boron nitride during co-infiltration steps describedherein. The porosity of the airfoil preform may be between about 10% andabout 90% by volume.

The tip preform and the airfoil preform may be infiltrated by aninfiltrate material such that a continuous blade 10 is formed. Thecontinuous blade 10 may be such that there is no stopping point,breaking point, or interruption between the airfoil 18 and the tip 12.Thus, the continuous blade 10 may be a monolithic piece or single piececonstruction. The infiltrated material may include silicon carbideand/or boron nitride. The infiltrated material may extend from theairfoil preform to the tip preform joining the tip preform to theairfoil preform. For example, the infiltrated material may extend fromwithin the airfoil preform to within the tip preform. The infiltratedmaterial may be substantially the same within the airfoil preform andthe tip preform such that a similar or substantially the same matrixmaterial is formed to join the tip 12 and the airfoil 18.

One illustrative method 110 for making a blade, such as the blade 10 foruse in a gas turbine engine described herein, is shown in FIG. 4. Themethod described herein is for making a blade, but it is understood anyrotating component with an abrasive surface in contact with an abradablesurface of a static component may be formed by the method describedherein. In a step 115 of the method of 110, a tip preform havingcontinuous porosity substantially throughout the tip preform is formed.The step 115 of forming a tip preform may include sub-step 120 of layingfibers, foam, or particles, sub-step 125 of encapsulating the fibers,foam or particles of the tip preform in a polymer, and sub-step 130 ofshaping the tip preform to conform to a shape of an airfoil preform. Thetip preform may have continuous porosity and may form a structuralscaffold for subsequent infiltration of a ceramic matrix. The sub-steps120, 125, 130 for forming a tip preform may be completed in any orderand not all sub-steps need to be used in all instances of forming a tippreform for use in a gas turbine engine.

In sub-step 120 of the step 115, the particles may be suspended in asubstrate or material comprising chopped fibers, continuous fibers,woven fabrics, and/or ceramic foam. Combinations thereof may be laid-up,fixed and shaped into the configuration of a desired component. Theparticles used to form the tip preform may be similar to materials usedin the airfoil preform and may include silicon carbide. In otherembodiments, the particle used to form the tip perform may be dissimilarto the materials used in the airfoil preform and may include cubic boronnitride, silicon nitride, or a combination thereof.

In some embodiments, after forming a layer of particles, other materialsor particles may be added to a layer of porous material. In someembodiments, the porous material may be a reticulated foam, includingbut not limited to a ceramic foam such as a silicon carbide foam. Areticulated foam may provide a porous substrate or structure which maybe constructed, arranged, or marked like a net or network. A reticulatedfoam may have a pattern of interlacing lines. The particles may be castinto the foam or porous substrate to form the tip perform. The poroussubstrate may be infiltrated by particles in subsequent steps.

In optional sub-step 125 of the step 115, the particles, fibers, and/orfoam are encapsulated in a polymer, as shown in FIG. 4. The polymer maybe one of polyesters poly (ethylene terephthalate), polyimide,polycarbonate, high-density polyethylene (HDPE), polyvinylidenefluoride, and polyvinyl chloride (PVC). The polymer may be used when thetip particles of the tip preform are dissimilar to the particles ofairfoil preform such that the two may not bind. The polymer mayencapsulate the dissimilar particles of the tip 12 to hold the particlesin position allowing the infiltrated materials to bind the tip preformand the airfoil preform. For example, the dissimilar particles mayinclude cubic boron nitride or silicon nitride. The polymer mayencapsulate or surround the particle and the porous substrate to providea shape for use in sub-step 130 of the method 100.

In sub-step 130 of the step 115, the tip particles, fibers, or/and foamare shaped to conform to the shape of the airfoil preform, as shown inFIG. 4. The tip preform may be machined to the shape of the airfoilshown in FIG. 3. In some embodiments, the tip preform may be machinedprior to an initial co-infiltrating step including densification viachemical vapor deposition (CVD) or chemical vapor infiltration (CVI). Inother embodiments, the tip preform may be machined after an initialinfiltrating step including densification via CVD or CVI.

In step 135 of the method 110, the tip preform is positioned relative toan airfoil preform. The tip preform may be inserted into a tip receivingspace, such as the tip receiving space 34 shown in FIG. 2. The tipreceiving space may be at the distal end 22 of the airfoil 18. The tippreform may be positioned to extend from inside the tip receiving spaceto beyond the distal end 22 of the airfoil 18.

In step 140 of the method 110, co-infiltrating of the tip preform andthe airfoil preform is performed, as shown in FIG. 4. Co-infiltratingmay include an optional sub-step 145 of burning off a polymer, and asub-step 150 of densifying the tip preform and the airfoil preform tofix the tip to the airfoil. The sub-steps of co-infiltrating may becompleted in any order and not all steps need to be used in allinstances of co-infiltrating the tip preform and the airfoil preform foruse in a gas turbine engine.

In sub-step 145 of the step 140, the polymer optionally included in thetip preform may be burned off, as shown in FIG. 4. The polymer may onlybe burned off if a polymer was added in step 125 of method 110. Burningoff the polymer may be performed by exposing the tip preform to heatwithin a furnace. In some embodiments, burning off the polymer may occursimultaneously with the sub-step 150 of densifying the tip preform andthe airfoil preform. In some embodiments, the polymer included in thetip preform may be burned off during an independent operation.

In sub-step 150 of the step 140, co-infiltrating includes densifying thetip preform and the airfoil preform. Densifying the tip preform and theairfoil preform may include CVD or CVI, slurry infiltration, and/or meltinfiltration. In some embodiments, the tip preform may be added to theairfoil preform prior to the airfoil preform undergoing CVD or CVI. Inother embodiments, the tip preform may be added to the airfoil preformafter the airfoil preform undergoes infiltrating via CVD or CVI.

CVD or CVI may be used to build up one or more layers on the ceramicfibers of the airfoil preform and the tip particle. The one or morelayers may include a silicon carbide layer. Furthermore, an intermediatelayers such as boron nitride may be deposited prior to the siliconcarbide layer. CVD may follow the same thermodynamics and chemistry. CVIand CVD may be non-line of sight processes such that CVI and CVD mayoccur completely within a furnace. The starting material for CVI mayinclude a gaseous precursor controlled by quartz tubes and may beperformed at temperatures between about 900° C. and about 1300° C. CVImay be performed at relatively low pressure and may use multiple cyclesin the furnace. Silicon carbide may also be deposited to build up one ormore layers on the fibers while the preform is in the furnace. Thesilicon carbide may provide additional protection to the fibers and mayalso increase the stiffness of the airfoil preform fibers and the tippreform. In some embodiments, boron nitride may be deposited prior thesilicon carbide to provide further beneficial mechanical properties tothe fibers. The preform may be taken out of the furnace after a firstpass through the furnace and weighed. If the preform is not at thetarget weight it may go through the furnace for another run, which mayoccur as many times as necessary in order to achieve the target weight.The target weight may be determined by the final part to be made. CVI orCVD may form a preform with a porosity of between about 40% and about50%. If the preform is at the target weight the part may undergo slurryinfiltration.

Once the tip preform and airfoil preform fibers are coated via CVI orCVD, additional particles may be infiltrated into the preformsconcurrently via other infiltration methods. For example, a slurryinfiltration process may include infiltrating the preforms with slurry.Dispersing the slurry throughout the preforms may include immersing thepreforms in the slurry composition. The slurry may include particles ofcarbon and optionally silicon carbide. The slurry may flow into thespaces, pores, or openings between the fibers of the preforms such thatthe slurry particles may uniformly impregnate the pores of the preformand reside in the interstices between the preform fibers. The slurryinfiltration process may form a preform with a porosity of between about35% and about 45%.

Prior to immersion, the preform fibers may optionally be prepared forslurry infiltration by exposing the fibers to a solution including, forexample, water, solvents, surfactants and the like to aid impregnationof the fibers. Optionally, a vacuum may be drawn prior to slurryintroduction to purge gas from the preforms and further enhanceimpregnation. Slurry infiltration may be conducted at any suitabletemperature such as at room temperature (about 20° C. to about 35° C.).The slurry infiltration may be enhanced by application of externalpressure after slurry introduction such as at one atmosphere pressuregradient.

After slurry infiltration, the tip preform and airfoil preform mayundergo melt infiltration. During melt infiltration a molten metal oralloy may wick between the openings of the preforms. In variousembodiments, the molten metal or alloy may have composition thatincludes silicon, boron, aluminum, yttrium, titanium, zirconium, oxidesthereof, and mixtures and combinations thereof. In some instances,graphite powder may be added to assist the melt infiltration. The moltenmetal or alloy may wick into the remaining pores of the preform throughcapillary pressure. For example, molten silicon metal may wick into thepores and form silicon carbide to create a matrix between the fibersresulting in a relatively dense tip 12 and airfoil 18 compared to thepreforms. For example, after the preforms have been densified, theairfoil 18 and the tip 12 may have a porosity of between about 1 percentand about 10 percent by volume. In one example, a temperature forinfiltration of silicon may be between about 1400° C. and about 1500° C.The duration of the infiltration may be between about 15 minutes and 4hours. The infiltration process may optionally be carried out undervacuum, but in other embodiments melt infiltration may be carried outwith an inert gas under atmospheric pressure to limit evaporationlosses. The co-infiltration processes described herein may create a tipjoined to an airfoil such that the tip 12 and the airfoil 18 are acontinuous structure.

In some examples the airfoil preform for blade 10 may formed by chemicalvapor infiltration. In other examples, the airfoil preform may be formedby a combination of chemical vapor infiltration, melt infiltration,polymer-infiltration-pyrolysis. In other examples, the airfoil preformmay be formed by a combination of chemical vapor infiltration andpolymer-infiltration-pyrolysis.

While the disclosure has been illustrated and described in detail in theforegoing drawings and description, the same is to be considered asexemplary and not restrictive in character, it being understood thatonly illustrative embodiments thereof have been shown and described andthat all changes and modifications that come within the spirit of thedisclosure are desired to be protected.

What is claimed is:
 1. A blade for a gas turbine engine, the bladecomprising an airfoil comprising a ceramic material defining continuousporosity, the airfoil having a distal end; a tip comprising a porous tippreform, the tip extending beyond the distal end of the of the airfoil;and infiltrated material that fills the continuous porosity of theceramic material of the airfoil and extends through the airfoil and theporous tip preform to join the airfoil and the tip, wherein a perimeterof the tip conforms to a perimeter of the distal end of the airfoil whenviewed from beyond the distal end of the airfoil.
 2. The blade of claim1, wherein the infiltrated material of the airfoil is the same as theinfiltrated material of the tip.
 3. The blade of claim 1, wherein theceramic material of the airfoil comprises silicon carbide, and the tipcomprises silicon carbide.
 4. The blade of claim 1, wherein the airfoilincludes a tip-receiving space that extends into the airfoil and aportion of the tip is arranged in the tip-receiving space of theairfoil.
 5. The blade of claim 4, wherein the airfoil includes a hollowcore in fluid communication with the tip-receiving space.
 6. The bladeof claim 1, wherein the tip further comprises tip particles suspended ina substrate.
 7. The blade of claim 6, wherein the tip particles includesilicon carbide.
 8. The blade of claim 6, wherein the tip particles areselected from cubic boron nitride, silicon nitride, or a combinationthereof.
 9. The blade of claim 1, wherein a porosity of the tip isbetween about 1 percent and about 10 percent by volume.
 10. The blade ofclaim 1, wherein the tip defines at least one cooling hole, wherein theairfoil defines a core, and wherein the core is in fluid communicationwith the at least one cooling hole.
 11. A blade for a gas turbineengine, the blade comprising an airfoil comprising a ceramicreinforcement material defining spaces between the ceramic reinforcementmaterial, the airfoil having a distal end defining a tip receivingspace; a tip comprising a porous structure defining spaces betweenmaterial of the porous structure, the tip being received in the tipreceiving space and extending beyond the distal end of the of theairfoil; and infiltrated material that extends from the spaces of theceramic reinforcement material to the spaces of porous structure to jointhe airfoil and the tip, wherein a perimeter of the tip conforms to aperimeter of the distal end of the airfoil when viewed from beyond thedistal end of the airfoil.
 12. The blade of claim 11, wherein theinfiltrated material of the airfoil is the same as the infiltratedmaterial of the tip.
 13. The blade of claim 11, wherein the ceramicmaterial of the airfoil comprises silicon carbide, and the tip comprisessilicon carbide.
 14. The blade of claim 11, wherein the tip furthercomprises tip particles suspended in the porous structure.
 15. The bladeof claim 14, wherein the tip particles include silicon carbide.
 16. Theblade of claim 14, wherein the tip particles are selected from cubicboron nitride, silicon nitride, or a combination thereof.
 17. The bladeof claim 11, wherein the tip defines at least one cooling hole, whereinthe airfoil defines a core, and wherein the core is in fluidcommunication with the at least one cooling hole.